[amsat-bb] Re: Since We Are Off Topic Somewhat....
vk3jed at gmail.com
Thu Feb 14 17:22:12 PST 2008
At 10:55 AM 2/15/2008, Joe wrote:
>How come, going up,, 0 to 17K MPh through the atmosphere, all is
>coming down,, 17K MPh to 0 unless it has protection it will burn up
>in the atmosphere from friction with the air.
I suspect if you look at the launch profile, you'll find that the
passage up through the atmosphere is relatively slow, and that the
bulk of the speed increase occurs above where the air density is
sufficient to cause problems.
Also, maximum acceleration is towards the end of the main engine
burn, due to simple physics. As the propellant is expended, the mass
of the vehicle is less, but the thrust remains roughly constant,
unless the engines are throttled back to reduce the G forces, as is
done with the Shuttle to minimise stress on the crew. This implies
that much of the speed increase occurs late in the burn, when you're
high enough to avoid significant friction heating.
73 de VK3JED
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